At the present time, drinking vessels of the same general type with which the subject invention is concerned are coming into use which is wide-spread and ever-increasing. Such drinking vessels are intended to receive either hot or cold liquids and are of a heat-insulating material. One class of such drinking vessels comprises a circular body having an open top and a removable lid. Vessels of this type are ordinarily discarded after one use. However, there is another class of drinking vessels which are of a construction which provides for their being used repeatedly. The instant invention is intimately related to this latter class.
Such drinking vessels may be characterized as including a circular body which may be either cylindrical or frusto-conical. But in either case, they present open upper ends. Secured to this upper end by a detachable connection is a top or cover consisting of a cylindrical wall and an inclined flat wall formed with a drinking opening adjacent to the periphery of the inclined wall and to which the lips of a user are applied as the contents of the vessel is imbibed.
If a hot liquid such as coffee is contained in the vessel, steam is generated which, if not removed or substantially eliminated, impairs the comfort of the drinker. Most of the cold drinks which would be received in the vessel are carbonated beverages which release carbon dioxide gas which, if not accommodated, will also impair the comfort of the drinker. Inventors, engineers and research workers in this field have recognized the desirability of alleviating the discomfort caused by hot or cold gases but most of these efforts have resulted in the provision of a relief vent in the cylindrical wall of the cover.
Obviously, valve members must be provided to close the drinking opening and the relief vent as the vessel is handled and carried about. Various mechanisms have been devised to maintain these valve members in closed sealing position. Some such mechanisms included lost-motion devices which caused the relief vent to open in advance of the drinking opening. In all such cases, the valve operating devices are highly complicated, difficult to produce in accordance with accepted manufacturing procedures, and therefore are expensive. Moreover, in nearly all of the known devices of this character, two springs are employed for the two valve members. In some instances, a single spring has been used, but this has resulted in uncertainty of operation and requires complex mounting structure for the spring.
While it has been proposed to provide the removable cover of a drinking vessel with a drinking opening and a relief vent, these known vessels are of the disposable type and do not include spring-biased valve members which are associated with the drinking opening and a relief vent in the inclined wall of the vessel cover.